The objectives of this work are to characterize a cholinergic synapse now almost certain to exist in the inner plexiform layer of a mammalian retina, and to seek an inhibitory synapse of the inner plexiform layer. Biochemical and electrophysiological experiments will study (1) the effect of acetylcholine depletion on ganglion cell responses, (2) the comparative pharmacology of the retinal acetylcholine receptor, and (3) the histochemical distribution of acetylcholine within the retina. A second series of experiments will assess the synthesis and release of possible inhibitory neurotransmitters, and will examine their possible interaction with acetylcholine in the electrophysiological responses of the ganglion cell. Studies of retinas from one day old rabbits, whose synaptogenesis is incomplete, suggest that during early development the ganglion cells have a sensitivity to acetylcholine which is qualitatively different from that of ganglion cells in adult animals. This possibility will be evaluated by correlating the progressing of ganglion cell responses to cholinergic agents with the morphological development of synapses and with the normal development of electrophysiological function.